This invention relates to tactile display device enabling tactile stimulation through vibration in human-machine interfaces such as communication of information to blind individuals and other touch based interfaces in equipments such as kiosks, mobile phones, and computer based gaming devices. Some aspects of the invention are applicable to an implementation of the invention integrating tactile display device with equipment called Talking Tactile Tablet (TTT or T3; U.S. Pat. No. 7,106,220) manufactured and offered in market by Touch Graphics Inc, NY. Further, and in addition, some aspects of the invention are applicable to another implementation of the invention integrating tactile display device with haptic equipment called Phantom® (product derived from U.S. Pat. No. 6,985,133) manufactured and offered in market by SensAble Technologies, Woburn, Mass. Other implementations of tactile stimulation including vibration for several other Human Machine Interface (HMI) purposes are also applicable.
Vibratory stimulation for use in communication such as vibration based message transmission, and human-machine interfaces such as enhanced experience during computer based gaming is a recognized need. Multi-point programmable tactile stimulation on human body can be a useful means for communication not only for persons challenged in receiving information through conventional visual or auditory means but also for general purpose applications. For example, there is emergence of vibratory tones in mobile phones to distinguish between the different callers so that the receiver of the call may identify the caller covertly without looking at the display of the mobile phone or listening to an auditory ring tone that disturbs others. In the gaming systems, there is growing need for increased sensory stimulation of different body parts of the gamers for multi-modal immersive feeling although currently the stimulation is mainly limited to vibratory joystick interfaces. In computer systems in general, tactile display that reads out information corresponding to an image visually appearing on a computer screen, and represents the image in the form of differential positions of the plurality of tactile output elements that provide a tactilely recognizable pattern representative of the information on the screen is a well identified requirement (for example, Tecu and Haas, U.S. Pat. No. 6,703,924 assigned to Hewlett-Packard Development Co, TX, wherein there is a mention of linear stepper motors as means to move plunger pins to realize the tactile display function without disclosing the detail how the required resolution, amplitude, and frequency of actuation may be achieved). Examples of these applications are found in the references in this provisional patent application, the contents of which are adopted herein in total by reference include: vibration by means of eccentric motor actuators (Yoshida et al, U.S. Pat. No. 7,157,822; Tremblay et al, U.S. Pat. No. 6,275,213), pressurized fluid actuators (Roberts et al, U.S. Pat. No. 7,352,356), dielectric elastomer actuators (Koo et al: Koo, I M, Jung, K, Koo, J C, Nam, J,-D, Lee, Y K, and Choi, H R, Development of Soft Actuator Based Wearable Tactile Display, IEEE Trans. Robot. 24, no. 3, pp. 549-558, 2008), and piezoelectric actuators (Gouzman et al, U.S. Pat. No. 5,912,660; Kyung et al, U.S. Pat. No. 7,339,574; Kyung, K,-U, and Park, J,-S, Ubi-Pen: Development of a Compact Tactile Display Module and Its Application to a Haptic Stylus, pp. 109-114, World Haptics 2007—Second Joint EuroHaptics conference and Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems, 2007, related technology patented as U.S. Pat. No. 7,339,574; Kim et al: Kim, S,-C, Kim, C,-H, Yang, G,-H, Yang, T,-H, Han, B,-K, Kang, S,-C, Kwon, D,-S, Small and Lightweight Tactile Display (SaLT) and Its Application, pp. 69-74, World Haptics 2009—Third Joint EuroHaptics conference and Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems, 2009).
The motor driven actuators based array systems suffer from constraints in miniaturization due to minimum size of motor and actuator elements that makes it difficult to embed them on a wearable substrate with the desirable flexibility and space resolution. The entire body of a motor and connected vibration device such as eccentric element vibrates instead of a desired specific area coming in contact with a human body.
The pressurized fluid actuators based system requires a complex grid of valves for control of actuation, again imposing difficulty in miniaturization, embedding, and achievement of close spacing.
The dielectric elastomer actuators are still in research and development, are not available in the market as a proved out product, require very high voltage through a high voltage switching circuit (3.5 kV for 0.471 mm amplitude of actuation), and moreover the center-to-center distance between adjacent stimulation points is currently about 3 mm (a grid of 20 actuator cells in a 4×5 matrix layout covers 11 mm×14 mm area) which is more than the desirable resolution as close as possible to 1 mm. The desirable resolution of 1 mm is well known in the field of tactile perception and established based on research and experiments on human perception reported as lateral two-point limen spatial resolution defining the minimal separation between two points that permits both to be perceived at a human finger tip (Biggs, J, and Srinivasan, Mass., Tangential Versus Normal Displacement of Skin: Relative Effectiveness for Producing Tactile Sensation, in 10th International Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems. Orlando, Fla.: IEEE Computer Society, 2002; Gulati, R J and Srinivasan, M A, Human Fingerpad under Indentation I: Static and Dynamic Force Response. Hochmuth, R M, Langrana, N A, and Hefzy, M S, Bioengineering Conference, BED-Vol. 29, 261-262, 1995; Sherrick, C E, Cutaneous Communication, in Neff, W D, Ed., Contributions to Sensory Physiology, vol. 6, pp. 1-43, Academic Press, NY, 1982).
It is found that piezoelectric elements that create enough perturbation amplitude reliably and in a repeatable manner for a long duration in a field application for useful tactile stimulation are long strips required to be deposed in cantilever configuration for desired vibration near the tip. Other type of piezoelectric actuators, such as for example screw type actuators (Henderson, U.S. Pat. Nos. 6,940,209; 7,170,214; 7,309, 943; 7,339,306) appear to be having limitations in terms of frequency of vibration, tend to get stuck at the ends of the stroke of the actuator, and additionally occupy lateral space due to required screw and nut components limiting center-to-center distance between the pins vibrating for tactile stimulation (the minimum housing nut cross section dimension currently is 2.8 mm square resulting in minimum possible center-to-center distance between adjacent pins to be about 3 mm). An alternative approach adopted by Kyung et al and Kim et al using disc based actuators called Tiny Ultrasonic Linear Actuator (TULA) that replaces screw by friction between disc hole and rod also has limitations in minimum center-to-center distance between adjacent pins that can be achieved because the actuators use piezoelectric bimorph discs that are 4 mm diameter and rods that pass through the center holes through discs are 1 mm diameter. Even by staggering the discs, the center-to-center distance between adjacent pins cannot be less than 2.5 mm. Moreover, these actuators need very high frequency generation circuit (for example, TULA-35 manufactured by Piezoelectric Technology, Seoul, S. Korea operates at 128 kHz frequency) and are primarily intended for displacement actuation as a friction based actuation substitute for screw based positioning, and as such do not appear to be ideally suitable for vibratory stimulation of human body parts with desired parameters of as close as possible to 1 mm spatial resolution and 50 Hz-500 Hz temporal resolution.
Our study and analysis has revealed that although piezoelectric actuation approach has been used in Braille displays so far, the current configurations are suitable for certain applications such as identification of a contact with a surface, for example, with a push button or pin and subsequent relative sliding motion between the contact and the surface to identify an adjacent button or pin that may be 3 mm or more distance apart; but they have many limitations that are restricting progress towards the type of configuration needed for wearable tactile display. A few of these limitations are as follows. As the piezoelectric actuators have very small amplitude of vibration, typically in the range of a few micro millimeters, they can be felt well desirably at frequency range 50 Hz to 500 Hz (the temporal resolution range for human perception is 0-1000 Hz as per the references cited in the context of spatial resolution in an earlier paragraph). The voltage requirements are ideally 100V and above, although there are attempts to use the actuators at lower voltages such as 25-30V with compromised lower displacement that is difficult to perceive. This is the main reason why the current devices use cantilever configuration to enhance the displacement to desirable amplitude in the range of 0.050 mm to about 1 mm. It is possible to accommodate the cantilever configuration if the communication of information is by numerous Braille cells and the finger slides over those cells as is the prevailing practice while reading cells in Braille Displays (for example, Brailliant Braille Displays manufactured and offered in North American market by Humanware Inc, Longueuil, QC, Canada). In such a configuration, center-to-center distance between adjacent pins is not required to be minimized and typically this distance is more than 3 mm. However, if we want to attach a cell on the finger and convey all the information through programmable actuation of the pins as required in wearable tactile display, a different configuration is required that has the potential to pack a higher density of actuators on a small footprint and lean package size with desired parameters of as close as possible to 1 mm spatial resolution and 50 Hz-500 Hz temporal resolution. It is also desirable that the voltage requirement is reduced to around 25-30V.
Aspects of the present invention overcome some of the difficulties in prior art either individually or in combination with each other. The advantages of the present invention will become apparent from the description and accompanying drawings.